Vibratile board for acoustic treatment



ea. 31, 1946., HURLEY 2,413,568

VIBRATILE BOARD FOR ACOUSTIC TREATMENTS Filed July 17, 1941 5 Sheets-Sheet l 84 INVENTOR AL ERT B. HURLEY FI -1.8 I

ATTORNEYS Dec. 31,1946. a HURLEY 2,413,568

VIBRATILE BOARD FOR ACOUSTIC TREATMENTS Filed July 17, 1941 5 Sheds-Sheet 2 INVENTOR ABERT B. HURLEY ATTORNEYS Dec. 31, 1946. A. B. HURLEY 2,413,568

I VIBRATILE BOARD FOR ACOUSTIC TREATMENTS Filed July 17, 1941 5 Sheets -Sheer, 3

Vii

INVENTOR AL ERT B. HURLEY BY M ATTORNEYS Dec. 31, 1946. A. B; HURLEY 2,413,568

VIBRATILE BOARD FOR ACOUSTIC TREATMENTS Filed July l7, 1941 5 Sheets-Sheet 4 Fig. 46

INVENTOR AL ERT B. HURLEY ATTORNE 5 ea. 31, 19%. A B. HURLEY 5 VIBRATILE BOARD FOR ACOUSTIC TREATMENTS Filed July 17, 1941 5 SheetsSheet 5 o ucooeooaooooooo 0000000000 0000000000000000000000 o A0090 nouoooeaooocoo -oooa oouoooonoooo c 2 2 0000 00000000 0 ocean cocoon o o 00000 00000 I a 000 ocooo o oooo0ooo0 onooo can a o oooouoo ooooao o cocoa 0000 o o o no a can a o 0 on o 0 26! o INVENTOR ALBERT B. HURLH Patented Dec. 31,1946

OFFICE VIBRATILE BOARD FOR ACOUSTIC TREATMENT Albert B. Hurley, Huntington, N. Y.

Application July 17, 1941, Serial No. 402,793

. 7 Claims. (01. ISL-33) This invention relates to the acoustic treatment of ceilings and walls for purposes of sound control.

The primary object of my invention is to generallyimprove the treatment of walls for noise absorption, or improved acoustics, or sound control in general. Another general object is to provide an improved tile or board for that purpose.

The science of sound control has undergone considerable development in recent years, and a number of companies manufacture tile or board of various kinds for this purpose. Some of these materials are matted wood fibre, porous gypsum, artificial stone using expanded mineral aggregate, mineral fibre or rock wool in pad or blanket form, baked rock wool and clay mixture, asbestos fibre appropriately cemented with or without the .admixture of other materials, etc. Some of these products rely solely on the porosity of the material, while others additionally provide holes in the material in an efiort to improve the sound absorption.

If the results obtained by the use of these materials is studied, it will be found that the sound absorption efficiency is substantially-greater for higher audible frequencies than for the low frequencies. One primary object of my invention is to improve the efficiency for low frequencies. With this object in view the tile or board is provided with peripheral cuts which separate the same into a marginal mounting portion and a vibratile center or diaphragm portion located within the marginal mounting portion. These peripheral cuts operate to weaken the connection between the diaphragm portion and the marginal portion in order to increase the flexibility of the connection, thereby facilitating vibration of the diaphragm portion, This enhances the dampening or absorption efiiciency of the board for low frequency sound.

An ancillary object of my invention is to particularly increase the flexibility of the connections, or as I term the same, the bridges between the marginal and diaphragm portions. With this object in view, I provide auxiliary cuts at the bridges transverse to the peripheral cuts, thereby lengthening and so increasing the flexibility of the bridges. When dealing with tiles of ordinary square dimension, it is most convenient to form the bridges by means of diagonal cuts at the corners of the tile.

A further object of my invention is to utilize known methods of improving the sound absorptionefliciency for high audio frequencies and for this purpose a number of different expedients may be employed, such as the provision of apertures in a thin tile made, for example, of enamelled sheet metal or plastic, or the provision of holes (round or elongated slots) part way through or all the way through a relatively thick porous tile made, for example, of wood pulp, matted wood fibre, porou gypsum, or the llke. Where the tiles are to be secured to furring strips, as is usually the case, a space is inherently provided in back of the vibratile diaphragm. In some cases, particularly with a thin perforated tile, it may be preferred to place sound absorbing pads or blankets made of a loose fibrous material such as mineral wool, in this space between the furring strips, but such pads are not at all essential with my invention, In rarer cases the tile may be cemented directly on a wall without furring strips, but in that case it should be provided with peripheral ledges, which are either added to the tile or molded integrally with the tile, in order to provide the necessary space in back of the diaphragm.

A further object of the invention is to obtain a more level response for the absorption of low frequencies, and for this purpose a number of tiles may be made, each having a diiferent natural resonance frequency. In one aspect, this object of the invention concerns provision of convenient methods of controlling the natural vibration frequency of the tile. The difierent frequency tiles may be applied to a wall or ceiling in appropriately staggered arrangement. In some cases, a predominant number of tiles of a particular frequency may be used, depending on the acoustic problem raised in any particular installation.

In accordance with a further feature of my invention, multiple diaphragms may be provided on a single board. Thus a large board may be sub-divided into, say, four diaphragms, each dimensioned as though formed in a board only half as long and half as wide as the actual board. This reduces the amount of labor attendant upon nailing up the boards. In other cases a small diaphragm may be formed at the center of a large diaphragm, thus providing a diaphragm resonant to one low frequency at the center of a larger diaphragm which is resonant to another low frequency,

Acoustic tiles having a diaphragm action are not broadly new, one such tile being made, for example, by Heerwagen Acoustic Decoration Company. However, such diaphragm tiles as have been made heretofore have been delicate 3 in structure and difiicult to apply, and while they may be helpful in eliminating some particular rumbling reverberation or booming sound, are

' little or not at all helpful for sound absorption of high audio frequencies. They sufier from the serious limitation of being useful only for low frequencies. Thus, while acoustic tiles are already available for high or low frequencies alone, their efiiciencies fall 01? very sharply for low or high frequencies respectively. With my invention, both low andhigh frequencies may be taken care of.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the acoustic tile features and their relation one to the other as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by drawings, in which:

Fig. 1 is a perspective view of a thin metal or plastic board showing the peripheral cuts to facilitate vibration;

Fig. 2 is a fragmentary view of one corner of a cast tile or pulp tile with a blind slot or groove therein;

Fig. 3 is a similar view, but showing a board having a through out and an elongated bridge;

Fig. 4 is a similar view showing a thin metal or plastic tile with a diagonal bridge; V

Fig. 5 is a similar view showing a cast or pulp tile with a diagonal bridge weakened by a longitudinal cut;

Fig. 6 is a similar view showing a tile with through cuts and a modified bridge;

Fig. 7 is similar, but with a further modification of the bridge;

Fig. 8 is a section taken in the plane of the line 88 of Fig. '7, and illustrates a method of further weakening or improving the elasticity of the bridge;

Fig. 9 is a similar section, but showing a modification in which the bridge of a relatively brittle cast tile is strengthened by means of an embedded metal reinforce;

Fig. 10 shows one corner of the upper side of a board in which the diaphragm portion is fully separated from the marginal portion but connected thereto by means of a spring bridge;

Fig. 11 shows a cast tile having a diagonal bridge strengthened by flexible means cemented thereto;

Fig. 12 is a section taken in the plane of the line l2-l2 of Fig. 11;

Fig. 13 is explanatory of how the boards of my invention may be secured to furring strips;

Fig. 14 illustrates how the marginal portions of a board may be thickened if the board is to be ce' merited to a wall;

Fig. 15 illustrates such boards cemented to a wall;

Fig. 16 shows how the boards may be provided with integrally thickened marginal portions;

Fig. 17: illustrates boards of this character ce-' merited to a wall;

Fig. 18 is explanatory of the fact that the various boards here illustrated, while shown with simple square edges, may be interlocked by appropriate known joints;

Fig. 19 shows how the diaphragm portion of a thick porous board may be provided with blind holes;

Fig. 20 is a similar view showing how the board may be provided with blind intersecting slots;

Fig. 21 shows a modification having through holes and an elongated diagonal bridge;

Fig. 22 is a modification having through slots;

Fig. 23 is a modification using biased or sloping slots;

Fig. 24 shows a modified arrangement of angular slots;

Fig. 25 illustrates a thin metal or plastic tile having through slots and perforations;

Fig. 26 is a similar view showing a thin tile having slots;

Fig. 2'7 shows how the thin tiles may be mounted on furring strips;

Fig. 28 is a modification in which the space between the furring strips is occupied by blankets or pads of mineral fibre or rock wool or like absorbent material;

Fig. 29 illustrates a modification using crossed furring strips; 7

Fig. 30 shows a laminated material made up of a thin metal or like hard-surfaced tile secured directly to a porous pulp tile;

Fig. 31 is a similar View in which the porous tile is slottedin registration with the perforations in the metal tile;

Fig. 32 is a section through a modification in which the metal tile is spaced somewhat from the porous tile, said section being taken approximately in the plane of the line 32-32 of Fig. 33;

Fig. 33 is a bottom plan view of the same;

Fig. 34 is a fragmentary section drawn to larger scale and showing a modification;

Figs. 35, 36, and 37 are fragmentary views showing how the resonance frequency of a tile may be varied by changing the length of the bridge or the width of the bridge, or both;

Figs. 38, 39, and 40 are sections taken longitudinally of the bridge (as in Fig. 8) and show how the resonance frequency of the tile may be changed by changing the thickness of the bridge;

Figs. 41, 42, and 43 are sections through a resilient bridge, and show how the resonance frequency of the tile may be changed by varying the length or the thickness of the resilient bridge, or

' both;

frequencies, one of these being used more than the other to fill the needs of a particularinstallation;

Fig. 48 shows how multiple diaphragms may be formed on a single large board to facilitate installation of the boards;

Fig. 49 shows how holes (to aid high frequency absorption) may be provided all over a tile including even the marginal portion thereof;

Fig, 50 shows a partially cut away composite tile in which a thick vibratile diaphragm is concealed by a highly perforate thin metal cover plate; and

Fig. 51 is a fragmentary section drawn to enlarged scale and taken approximately in the plane of the line 5 |-5l of Fig. 50.

Referring to the drawings, and more particularly to Fig. 1, I there show a board or tile I2 made of thin hard material. It may, for example, be made of metal appropriately painted or enamelled. It may also be made of a thermoplastic material, such as Bakelite or other similar plastics, from which boards or panels are made by impregnating fabric, paper, or wood veneer. In accordance with my invention the tile is provided with peripheral cuts l4, I6, I 8, and 20. These divide the tile into a marginal mounting section or portion 22 and a center or diaphragm section or portion 24. The marginal mounting portion may be secured to furring strips or the like, by means of nails, screws, or other suitable fasteners. Because of the peripheral cuts the diaphragm portion 24 may vibrate readily relative to the marginal portion. This vibration under the impact of low frequency sound waves serves to dampen and absorb the sound waves. The cuts are not continuous, the interruptions therebetween leaving rigid and flexible spaced connections 26 which may be termed bridges.

Referring now to Fig. 2, I there show one corner of a tile or board which may be made of a suitable porous material. Known commercial materials may be used, such as those made by the Celotex Corporation which makes Acousti-Celotex out of perforated fibre, Mufiietone out of cast porous gypsum, Calicel which is an artificial porous stone made out of expanded mineral aggregate, and Absorbex made out of matted wood fibres. Other suitable materials are made by Johns-Manville Corporation, who make Permacoustic out of baked rock wool and clay; Spongecoustic out of asbestos fibre, natural sponge, and cement; Fibretex which is made out of wood fibre; Transite which is made out ofasbestos and cement; and Airaco-ustic which is made out of rock wool and a suitable binder. A number of other companies make sound absorbing tiles or boards including Armstrong Cork Company, National Gypsum Company, and United States Gypsum Company.

In accordance with the present invention, the tile 30 is peripherally cut or slotted as indicated at 32 and 34. In the present case, the slots do not go all the way through the board and therefore the cuts may be continuous, the connection between the diaphragm portion 35 and the marginal mounting portion 38 being provided by the uncut thickness indicated at 40.

In Fig. 3 I show a board or tile in which the diaphragm portion 42 is adapted for freer vibration relative to the marginal mounting portion 44. This result is obtained by the use.of through cuts 46 and 48 which are not connected end to end, thus leaving a bridge 50. In the present case, an additional cut 52 is provided parallel to but spaced from the cut 48, thus elongating the bridge 50 and so increasing its flexibility. This, of course, makes the diaphragm portion 42 more readily vibratile.

In Fig. 4, I show a tile of the thin hard variety, such as metal or plastic, but in this case the bridge 52 between the cuts 54 and 56 is elongated by the use of diagonal cuts 58 at each side of bridge 52. This obviously increases the ease of vibration of the diaphragm portion 6!].

Fig. 5 illustrates a thick porous tile having cuts or slots 62 and 64 which pass nearly but not wholly through the thickness of the material. A diagonal bridge is provided at each corner, this being formed by diagonal cuts 66, and the bridge may be further weakened for improved vibration by a diagonal center cut 68 extending longitudinally of the diagonal bridge 6 and dividing the same in effect into two narrower bridges.

Fig. 6 illustrates a thick porous tile, the diaphragm portion 10 of which is connected to the marginal mounting portion l2 by means of a diagonal bridge 14 formed by diagonal slits 15. These, as well as the main cuts 18, pass all the way through the material. In this case the diagonal cuts 16 extend outwardly from the peripheral cuts 18.

In Fig. '7 the diagonal cuts 88 extend inwardly and outwardly of the peripheral cuts 82, thus providing an elongated bridge 84 which yieldably connects the diaphragm portion 86 to the marginal mounting portion 88.

Fig. 8 illustrates how the diagonal bridge may be further weakened for freer vibration, particularly when dealing with a thick tile or board. In Fig. 8, which is a section taken longitudinally of the bridge 84 in Fig. 7, it will be noted that the bridge portion 84 is cut away at the back, as is indicated at 90. This constitutes another means for controlling the vibration of the diaphragm portion, particularly when dealing with thicker or stiffer materials.

Some materials, such as cast gypsum, may prove to be troublesome because of their brittle or frangible nature. Thus with tiles having 9, diaphragm portion connected to the marginal portion solely at the corner bridges, difiiculty may arise because of breakage of the bridge during shipment or handling. This difficulty may be overcome by reinforcing the bridges, and one method of doing this is illustrated in Fig. 9 in which a, sheet metal strip 92 preferably made of resilient material, such as spring metal, is embedded in the tile at the bridge during casting of the tile. If desired, the ends of the spring metal may be bent to form spacers or feet 94 on which the reinforce 92 may rest in the mold during the casting operation. It will be understood that the section of Fig. 9 is taken longitudinally of the bridge, or in the same direction as Fig. 8, and that the metal reinforce 92 is simply an elongated rectangular strip disposed longitudinally of the bridge.

A simpler method of reinforcming the bridge is that illustrated in Figs. 11 and 12 in which the reinforcing strip 96 is simply cemented to the bridge 98 on the upper or inner face of the tile. In the present example the reinforcing strip 96 is a thin strip of wood.

If desired, a thin strip of flexible material, such as spring metal, may be used as the entire bridge. An example of this is shown in Fig. 10 in which the diaphragm portion I00 is completely separated from the marginal portion I92 by means of a continuous peripheral cut IM. They are again connected together, however, by means of spring metal strips I06 secured thereto by suitable means such as screws. The resulting bridges may be located diagonally at the corners of the tile, as shown in Fig. 10, and, of course, are preferably located on the back or inner surface of the tile the tiles are sufliciently-wide to bring theperipheral cuts within or between the furring strips or, in other words, to localize the diaphragm portion to the space between the furringstrips, so that the diaphragm portion, is freely vibratile.

While in the preceding and succeeding illustrations I. show the tiles with simple square edges, it will be understood that any of the known interlocking edges may be employed in order to give the finished wall or ceilin a more ornamental appearance, and in order to conceal the nails and to facilitate fastening the tiles in place. Many such interlocking connections are already known, and a typical one is that illustrated in Fig. 18, in which two adjacent edges of; each tile are providcd with a male edge IIIl, while the other two edges have a mating female edge 2. These fit together in a manner clearly shown in the drawings, and leave an ornamental V-shaped scoring I I4, exposed to the eye.

In some cases it may be more convenient to secure the sound absorbing tiles directly to a wall as by means of cement, without using any fur-ring strips. portion of the tile is preferably thickened on the back in order to provide at least a little space to accommodate the vibration of the diaphragm portion, and to provide a sufiiciently large air space therebehind.

In Fig. 14 an ordinary flat tile is shown thickened at its side edges by the addition of strips of material H6, these being cemented to the two opposite marginal portions of each tile as a part of the manufacture of the tile. The other two edges have been left open, for free air movement. Fig. 15 illustrates the attachment of these tiles to awall I I8.

In Fig. 16 I show a more advanced and preferable arrangement in which the thickened marinal portions I29 are formed integrally with the remainder of the tile by appropriate shape of the mold used to manufacture the tile. These tiles are shown cemented to a wall or ceiling I 22 in Fig. 17. In Figs. 15 and 17 the clearance shown has been minimized, and in many cases a larger air space may be wanted, and can. of course, be provided. Also ledges may be provided on all four edges, if it isdesired to isolate the action of each tile.

As so far described, the tiles are peripherally cut and are so mounted as to afiord vibration of most of the area of the tile for purposes of improving the efiiciency of the tile for dampening low frequency sounds. High frequency sounds may be absorbed or deadened by the porous nature of the material from which the tile is made. If desired, however, the efficiency of the tile for absorption of high frequency sounds may be enhanced by the provision of suitable holes (by which term I include also slots) out part way or all the way through the tile.

Specifically, in Fig. 19 the diaphragm portion I24 is provided with holes I26 which pass part way through the material. The spacing, diameter, and depth of these holes may be selected in accordance with known methods heretofore developed in connection with-similar boards already made in a commercial way, but, of course, devoid of the peripheral cuts I23 for facilitating vibration of the center portion acting as a diaphragm to dampen low frequencies.

Fig. 20 is a modification in which the holes for improving the eiiiciency of the unit for, high frequency take the form of elongated slots I It arranged transversely to another series of elon- For this purpose the marginal mounting.

8 gated slots I32. These are in addition to; pe ripheral cuts I34 which free the diaphragm portion for vibration.

The holes for high frequency sound absorption may pass entirely through the tile, and this is illustrated by the holes I36 shown 1 2 Fig; 213. This figure, incidentally, illustrates the use, of diagonal cuts I38 to elongate the bridge I548 between the peripheral cuts IdZ. 1

In Fig. 22 the holes for high frequencydissipation take the form ofthrough slots M4, With through slots, it is, of course, not possible to use transversely arranged slots as shown in, Fig. as. In Fig. 22 th peripheral cuts I46 lead to a bridge I48 Which extends parallel to. one side of the tile, rather than diagonally thereof. The bridge is elongated by means ofan extra. cut I553;

Fig. 23 illustrates a porous board having pe-v ripheral cuts 552 and slots for high frequency sound, these slots being disposed at an angle relative to the plane of the tile. There are slots. I5 3 which slope toward the left, as viewed in Fig. 23, and slots I56 which slope toward the right. These intersect at a common opening I53.

Fig. 24 is similar, except that the oppositely sloping slots ace, I62 are entirely separate from one another. 7

Fig. 25 shows a thin material such assheet metal or plastic provided with peripheral cuts I64, diagonal cuts I 66 forming an elongated bridge I63, and perforations Il-t! to improve the efiiciency for high frequencies.

In Fig. 26 there are peripheral cuts I'I;2 to

- divide thetile into a center diaphragm portion Il and a marginal mounting portion I'It. In; stead of perforations the tile portion I'M has slots H3. In the case of a thin material, such as that shown in Figs. 25 and 26, the improvement in high frequency dissipation is due to the passage of sound through the perforations into the space in back of the tile where the sound is reflected, dissipated, and absorbed. Thus the. tile should be spaced from the wall not only to afford vibration of the diaphragm, butfalso to improve the dissipation of high frequency sound. This is illustrated in Fig. 27, in which furring strips we are preliminarily secured to a wall I82, following which the thin tiles I84 are secured to. the furring strips. The titles we may have the features of Fig. 25 or Fig. 26, or any desired combination of these features.

Instead of using an unoccupied air space in back of the tile, this space may be filled by a fibrous material such as mineral fibre or rock wool. These materials are now made in the form of pads or blankets which may be laid between the furring strips, as is indicated at I85 in Fig. 28. In other respects, Fig. 28 corresponds substantially to Fig. 27.

In Fig. 29 I illustrate a modified arrangement in which the pads or blankets 0r fibrous material may be held in position by additional fur-1 ring strips. Specifically, a series of parallel furs ring strips I38 are preliminarily secured to wall I88 in spaced relation. The pads or blankets I32 are laid between the furring strips I81; and are held in position by fastening transverse furring strips I94 to the furring strips I58. The fur ring strips I88 are properly spaced to receive the previously made up pads 0r blankets. The furring strips I95 are properly spaced to properly fit the tiles IE6. These tiles may have the features of Fig. 25 or Fig. 26, or any desired combination of these features.

In some cases it may be desirable to employ a laminated tile made up of a thin hard surface material and a thick porous material. For example, the sound absorbing property of the thick porous material may be wanted together with a sanitary washable surface as, for example, in hospitals or the like. Such a tile is shown in Fig. 30, it comprising a thin hard material 206 cemented to a thick soft porous material 202. The combined or laminated board is peripherally cut at 204 in order to free the center portion for vibration. The center portion of the thin lamination is perforated as is indicated at 206, thus admitting sound to the porous material where it tends to be absorbed.

Fig. 31 shows a modification in which the thick porous backing material 208 is slotted at 2), these slots being disposed behind and registering with the holes 2| 2. This improves the efficiency with which sound is admitted to the porous backing material.

With the tile shown in Figs. 30 and 31 a space must be provided in back of the diaphragm to afford vibration of the same. This is readily done when the tiles are to be secured to furring strips. If the tiles are to be cemented directly to a wall, then it is necessary to provide thickened edges as was described in connection with Figs. 14 through 17. However, a modified tile may be made in which the thin surface material vibrates while the thick porous material is cemented directly to the wall. Such an arrangement is shown'in Figs. 32, 33, and 34. In this case the laminated tile comprises a thin hard surface material which is dished or bent near its periphery to displace it from the porous backing material. Specifically, the complete tile comprises a porous back 2| 4 and a metal front 2|6, the latter being bent at 2|8 to space the diaphragm portion from the backing board. The metal or outer material is peripherally cut as is indicated at 220, thus freeing the diaphragm portion for vibration. The parts may be secured together by the use of eyelets 222, these being convenient because nails and screws for securing the laminated tile in position may be passed through the eyelets. However, the present form of tile is ideally suited for cementing to Walls because the entire back of the porous tile may be cemented to the wall. Low frequency sound tends to be dampened by vibration of the diaphragm, while high frequency sound passes through the perforations and is dissipated in the porous material.

Fig. 34 illustrates a modification in which the backing board 224 is provided with parallel slots 226 to aid in the absorption of high frequency sound in the porous material. These slots may register with the lines of holes 228 through the sheet metal diaphragm, but such registration is not essential because of the space between the sheet metal surface material and the porous material.

An advantage of the laminated forms of the invention shown in Figs. 30 and 31 is that the boards are imperforate in respect to low frequencies, thus obtaining maximum efficiency of vibration a a diaphragm. From the viewpoint of theory and the gathering of performance data, it is a simplification to use an imperforate diaphragm, and from this viewpoint the peripheral cuts which free the diaphragm from the marginal portion should preferably be thin slits rather than wide slots, that is, there should be little appreciable width to the out if the cut is separate resilient bridge member.

a through one. This helps divide the action of the tile as a diaphragm, on the on hand, and as an absorption medium, on the other. With through holes in the diaphragm the theory becomes more complex. Much previously known data on the absorption of high frequencies may be employed while using blind holes or slots.

In making the above observation, I do not mean that it is undesirable or unsatisfactory to use through perforations or through slots to aid in the absorption of high frequencies. I mean merely that the performance of the diaphragm as a diaphragm for the absorption of low frequencies will be affected by an appreciably extensive area of through perforation, and the performance data must be appropriately modified.

While peaking of performance characteristics of the tiles, it may be well to point out that the air space in back of the tile affects the natural resonanc frequency of the diaphragm. Thus, if the performance data of a particular tile is obtained while mounting the tile on furring strips which are two inches thick, the tile should afterward be used on similar furring strips which will similarly space the tile two inches from the wall. A change to a spacing of only one inch from the wall will change the performance of the tile. In general, a substantial space is better than a small space where structural considerations make the use of a substantial space feasible. Also a free movement of air in back of the tiles is thought desirable by many.

In actual practice a number of different tiles are preferably provided having different natural resonance frequencies. This is desirable in order to level off the absorption of low frequencies over the entire low frequency range. For example, there might be five different frequency tiles all in the low frequency range. As a random example they might respond to or peak at 64, 128, 256, 334, and 512 cycles, respectively.

This different frequency response may be obtained by making the bridges wider or narrower or by making them longer or shorter, or by making them thicker or thinner. Thus, referring to Figs. 35-37, I there show three tiles which are similar, except that in Fig. 35 the bridge is long; in Fig. 36 it is of medium length; while in Fig. 37, it is short. In Fig, 35 the bridge is narrow; in Fig. 36 it is of medium width; and in Fig. 37 it is wide. Either or both of these changes in dimension may be employed with a view to changing the flexibility of the bridge, and thereby changing the natural resonance frequency of the tile.

In Figs. 38, 39, and 40 I show sections through the bridge (generally similar to the section shown in Fig. 8) but in Fig. 38 the bridge is of minimum thickness; in Fig. 39 it is 0f medium thickness; and in Fig. 40 it is of increased thickness. The bridge of Fig. 38 is more flexible, and that of Fig. 40 is less flexible, than that shown in Fig. 39.

In Figs. 41, 42, and 43 I show how the same adjustment may be made with a tile having a In Fig. 41, the bridge 233 and the undercut 232 therebeneath are short; in Fig. 42 the bridge 234 is of medium length and the same applies to the undercut 236 therebeneath, while in Fig. 43 the bridge 238 is of maximum length and the same applies to the undercut 240 therebeneath. Thus the bridge of Fig. 41 will be less yieldable and that of Fig. 43 will be more yieldable than that shown in Fig. 42. In this form of the invention the diaphragm 242 is out free of the marginal portion 244 by ll niean sfof the penpiierm cut '24s. The undercut bneaththe bridge provides clearance to accommodate flexing of the spring "strip. The end portions of the bridge beyond the undercut are secured fto the material of the til in any suitable manner, as by cementing the same in position. Instead of changing the length of the resilient bridge it may be changed in width (not shown but analogous to Figs. 35-37) or it may be changed in thickness. This is illustrated in the drawings in which the bridge of Fig. 41 is thicker and the bridge of Fig. 43 is thinner than that shown in Fig. l2. It will be understood that any one or more of these methods of changing the natural resonance frequency of the tile may be employed. It will also be understood that while three different dimensions have been illustrated, ajg'reater number may be employed, and in practice it may prove desirable to'h'ave, say, five "different frequency tiles.

V For a uniform response these may be arrangedin staggered relation, one such relation being shown in Fig. 45, in which the tiles marked 1, 2 3, 4, and correspond to five different frequencies. It will be understood that each of these tiles is provided with peripheral cuts and bridges for the diaphragm action, and is preferably provided with holes for high frequency absorption. It will be noted that tlie first horizontal row is arranged in 's'equ'encefrom 1 through 5; that the same applies to the second horizontal row, except that it begins with tile No. 3; while the thirdhorizontal row begins with tile No. 5; the fourth horizontal row begins with tile No. 2; the fifth horizontal row begins with tile No. 4; and the sixth horizontal-row repeats the first horizontal row, that "is, it begins with le i In most cases the acoustics of a room or hall may actually be measured before the sound absorbing treatment is applied thereto. In such case it may be found that increased corrective use of a certain frequency tile is needed relative to the other tiles. Thus in Fig. 46 it is assumed that the number of No. 1 tiles is to be doubled. Each horizontal row is shown arranged with a No.1 tile between the No; 3 and No. 4 tiles,thus doubling the number of N0. 1 tiles, but distributing the same uniformly. The succeeding ro'ws'begin with di'iferent tiles as, for example, the order shown in which the sequence vertically is the same as that horizontally. Other arrangements may, of course, be employed. e

In measuring the acoustics of a room, it may be found that only one or two different frequency tiles are needed, and it may be found that one of these is needed more than the other. Such a situation is illustrated in Fig. 47, in which thetile is being treated with only the No. 2 and No. 3 tiles, and with twice as many No. 3 tiles being used as No. 2 tiles. These may be appropriately staggered in any desired relation.

I In. practicing the present invention, it is possible to so cut a large board or tile as to form more than one diaphragm therein. Such an arrangement is shown in Fig. 48 in which the wall has furring strips 250 and is covered with boards 252 which are, say, four feet square. This board is so cut as to form four diaphragms 254 which correspond in size to what would normally be usedfwith a two foot tile. This facilitates and speeds up the operation of covering a ceiling or walls, because only a smaller number of boards must be secured in position. Furring strips may be used on two foot centers, thus supporting the 12 large board at the middle aswellaspat the edges. It ispossibie to, va ih jh dse of thej ol r d afih m h 'n ovid ii ur f erent f uency phragm, Onja singleboard. However, for the sake of simplicity, and in order to permit of flexibility in installing any desired frequency v diaphragrns in any desired proportion for each problem, one may make the four diaphragms inFig. 48 alike, the large board then acting, as a nest of four diaphra'gms all having a common resonance frequency. I I m y H g In Fig. 44 I showa different arrangement having more th'anon'e diaphragm formed on a single board. In this'case thereis a rather small diaphragm 26.0 located atthe center of a large diaphragm 262. The small diaphragm maybe designed to have a natural resonance frequency in the high part'of the, low frequencyrange, while the large diaphragm 262 maybe designedto have a natural resonance in the low partjof the low frequency range, All these diaphragms may be provided with holes 2 6 4jto aid high frequency absorption. In the specific case'h'elfe s'hown the ho s. eel n at d, bl n o s. arran d i crossed formation. It will be understood, however, that round 'holesmay 'be useiand that the holes maybe locatedfin the marginal as well as the diaphragm portions of the complete tile. v

49 a b ref rre o Sh wing th i o furn sh f e u nlcytabso nt n pp ied a l over a tile including the marginal portion as well as thediaphragm portion. This niay'fbe fd'one becausethe operation inre'spect to'highfrequencies doesnot depend upon the diaphragm vibration. C )veralluse of holes provides a'more uniform surface appearance for the wall, which'm'ay be ofadvantage in some instances. I I I Figs. 50 and51 show anarrangement in which a thin (for example, metal) surface 'materialIZSl is combined With athick absorbent materm 2,63, thefirnetal beingfdished at 1265 and secured to the tile 263, as by means of eyelets 26 6. The'cbmplete tile istmounted on furring strips 258, so as to be spaced from the all in order to afford vibration of the thick absorbent material 263. This'i'speripnerally cut as indicatedfat 210, and may, beplQi i'ded with diagonal cuts and'bridgs, all as previously d'escri'b'eol. The jinet'al covering plate Zfil', however, is not provided with peripheral cuts andneed not vibrate. It is made very highly perforate, as isindicated by the closely spaced holesjZTjZ, It is madeso highly perforate as to afford adequate free ransmission of low frequencies, which their cause vibration of the diaphragm263,'there'being nofapfofeciabl'e vibration" of jthesurface material or eeve'rm plate 26 I. This, howeve gmayb'e used in order to present an attractive enamel finish where such a finish is desired, There 'is'al'so thebe'nefit'of having two air spacesfbecause some high frequency sound absorptiontakes p1ace in ,the 'air space between the laminations 28l ar'id263. e Itwill be understood that one of the factorsin determining the natural resonance frequency of the t ilejis the mass of the vibrating diaphragm. This depends on its size and thickness as well as on the "density of thematerial. Thus in Fig, '44 thediaphragrn 262 hasfa much larger mass than e "d aphragm 2 9, which, in turn, results in a difference in resonance frequency.

N There: is a conflict of opinion as towheth'er the air space in back of the vibrating diaphragm shouldfor shouldn'ot be sealed. some authorities sa'y thatthere should preferably be a cornmunicationfr'om one tile to the next. This is obin back of the tile may be left vacant aeragqs tained by using furring strips without any cross pieces which might interfere with free flow of air in the longitudinal spaces between the furring strips. Similarly, when pieces are cemented to the back of a tile as in Fig. 14, they are desirably cemented along only two edges, rather than all four edges, The same applie when using molded edges-as in Fig. 16, but in this case it is also possible to simply interrupt the edges to form sev eral short well-spaced projections along all four edges. However, if it is desired to isolate the effect of each tile, then cross-pieces must be used, or in the case of Figs. 14 and 16, the raised edges should extend entirely around the periphery of the tile. One treatment may be better for sound absorption, say, at the back of an auditorium, and the other may be better for sound reflection, say, at the stage, but this difference is not critical to my invention, which is applicable to either the open or the sealed treatment.

It is believed that the method of making and using my invention, as well as the advantages thereof, will be apparent from the foregoing detailed description. The improved board or tile acts as a diaphragm and vibrates under the impact of low frequency sound waves. It dampens the waves, the energy being dissipated in the bridges. The high frequency waves pass into or through the diaphragm and are there deadened or dissipated. The improved tile corrects one of the important defects of previously known tiles, namely, the fact that they are efiicient over only one end or the other of the audio range. With my improved tile the best known efficiency for high frequencies may be retained without loss, and eiiicient operation in the low frequency range is superimposed on that. Relatively free vibration of tiles made of known materials is obtained in comparatively simple fashion by the use of peripheral cuts which free the center or diaphragm portion from the marginal or mounting portion. The resulting spaced bridges may be made more flexible by elongating them, or thinning them, or both, and if necessary the bridges may be reinforced to strengthen the same. The tiles may be mounted on furring strips or may be provided with thickened edges and mounted directly on a wall. Holes may be provided to improve the absorption of sound and these may be round or elongated and may pass part Way through or entirely through the tile. The space or may be filled with a fibrous material Such as mineral or rock wool. The tile may be laminated of several materials, and if desired one of these may be vibrated relative to the other. In all cases the edges of the tiles may be appropriately shaped to form interlocking joints.

Tiles having different natural frequencies may be provided, and different selections and proportions of these tiles may be used in accordance with the requirements of any particular installation. Multiple diaphragms may be formed in a single tile or board. Holes for high frequency response may be formed in the diaphragm or the marginal portion or both.

It will therefore be apparent that while I have shown and described my invention in a number of preferred forms, many changes and modifications may be made in the structures disclosed without departing from the spirit of the invention, as sought to be defined in the following claims. In the claims the term peripheral cut is intended to apply to a cut which frees the diaphragm portion for vibration, whether these cuts extend part way or all the way through the ma= terial. The term bridge is intended to mean any connectionwhich holds the di p p tion to the marginal mounting portion, whether or not elongated. The expression hole in connection with high frequency absorption is intended to include either a through hole or a blind hole, and either a round hole or elongated hole such as a slot.

I claim:

1, An acoustic tile comprising a central enclosed vibratile diaphragm section and a marginal diaphragm-enclosing mounting section, the diaphragm section being inwardly spaced from the mounting section by a peripheral opening therebetween, the diaphragm section being rigidly connected to the mounting section by bridge elements bridgin said peripheral opening, the diaphragm section thereby forming a vibratile member freely set into vibration at said rigid bridge elements on the mounting section under the impact of sound waves, the free vibration of said vibratile member serving to absorb the said sound waves.

2. An acoustic tile comprising a central enclosed vibratile diaphragm section and a marginal diaphragm-enclosing mounting section, the diaphragm section being spaced inwardly from the mounting section by peripheral diaphragm-defining cuts, the diaphragm section being rigidly connected to the mounting section by bridge elements bridging said peripheral cuts, the diaphragm section thereby forming a vibratile member freely set into vibration at said rigid bridge elements on the mounting section under the impact of sound waves, the free vibration of said vibratile member serving to absorb said sound waves.

3. An acoustic tile comprising a central vibratile diaphragm section and a, marginal diaphragm-enclosing mounting section, both sections being made of the same material, the diaphragm section being spaced inwardly from the mounting section by peripheral diaphragm-defining cuts produced in said material, the diaphragm section being rigidly connected to the mounting section by bridge elements bridging said peripheral cuts, the diaphragm section thereby forming a vibratile member freely set into vibration at said rigid bridge elements on the mounting section under the impact of sound waves, the free vibration of said vibratile member serving to absorb said sound waves.

4. An acoustic tile comprising a central enclosed vibratile diaphragm section and a marginal diaphragm-enclosing mountin section, the diaphragm section being spaced inwardly from the mounting section by peripheral diaphragmdeflning cuts, the diaphragm section being rigidly connected to the mounting section by bridge elements bridging said peripheral cuts, the diaphragm section thereby forming a vibratile member freely set into vibration at said rigid bridge elements on the mounting section under the impact of sound waves, the free vibration of said vibratile member serving to absorb said sound waves, the said bridge elements being provided with cuts transverse to the peripheral cuts to lengthen and thereby increase the flexibility of the bridges.

5. An acoustic tile comprising a central enclosed vibratile diaphragm section and a marginal diaphragm-enclosing mounting section, the dia phragm section being spaced inwardly from the mounting section by peripheral diaphragm-defining cuts, the diaphragm section being rigidly cona r-ra ses nected to the mounting section by 'bridge "elements bridging said peripheral cuts, 'the diaphragm section-thereby forming -'a 'vibratile member freely set into vibration at said rigid ibridge elements on the mounting section under-the impact of sound Waves of relatively low frequency, the free vibration of said vibrat'ile member serving to absorb said sound waves, the said, diaphragm being provided with holes inorderto increase the absorption of high frequencysound.

6. An acoustic tile "comprising a central -enclosed vibratile diaphrag-msectionand ama-rginal diaphragm-enclosingmounting section, both-sectionsbeing made of *the same material, the'diaphragrn section being spaced inwardly 'fromthe mounting section by peripheral diaphragm defining cuts produced in saidmaterial, thediaphragm section being rigidly connected to themounting section by bridge elements bridging said peripheral-outs, the'diaphragm section therebyforming a vibrati-le *member freely set into vibration at said rigid bridge elements 0n the mounting section un'de'rthe impact of sound waves, the free vibration of said vibratile mem'ber serving to absorb said soundwaves, the said bridge-elements having predetermined dimensions to predetermine -the Vibration period o'f-said diaphragm.

7. :An acoustic tilestructure comprising. in combinationa plurality of acoustic tiles as defined in claiinl, in which the diaphragm sections are connected to the mounting sections solely by means of the bridge elements, and in which the bridge elements-of difrerenttiles-are of different dimensions in order to vary the natural resonance frequency of some of the-diaphragms relative to other diaphragms.

ALBERT 'B. 

